The eye is an organ in which transparency should be maintained. An eye is supplied with oxygen to keep the eye healthy. However, the absence of blood vessels in the eye tissue requires that oxygen be supplied to the eye cells directly from the atmosphere through the cornea, rather than through the blood.
When worn on the eye, contact lenses significantly impede the oxygen supply to the cornea. In particular, extended wear of contact lenses can result in oxygen depletion in the cornea, causing eye diseases such as redness, corneal edema and vascular invasion. For this reason, the oxygen permeability is particularly important among other properties of contact lenses as it affects the oxygen supply to the eye cells.
Hard contact lenses (RGPs) and unhydrated soft contact lenses have high oxygen permeability due to their silicone component. Nonetheless, the high lipophilicity and water-repellency of the silicone component tend to make these contact lenses less lubricious and susceptible to adhesion of lipids and proteins. In this respect, the adhesion of lipids and proteins to contact lenses can cause problems such as foreign body sensation and low visibility. To address these issues, various surface modification techniques have been proposed in order to prevent the adhesion of lipids and proteins and improve the surface wettability in contact lenses comprising a silicone component.
For example, Patent Document 1 listed below (the entire disclosure of which is incorporated herein by reference) discloses a method for modifying a surface of an ophthalmic lens with a graft polymer by subjecting an ophthalmic lens substrate to a plasma treatment to generate radicals on the treated surface of the ophthalmic lens, and subsequently immersing the ophthalmic lens in a monomer solution for polymerization.
Patent Document 2 listed below (the entire disclosure of which is incorporated herein by reference) discloses a method for making a surface of a soft resin device hydrophilic by alternately laminating the surface of the device with an acidic polymer and a basic polymer.
Patent Document 3 listed below (the entire disclosure of which is incorporated herein by reference) discloses a method for modifying a surface of an ophthalmic lens by preparing in advance a polymer surface modifying agent having any desired terminal functional group by using the atom transfer radical polymerization (ATRP) technique or the reversible addition-fragmentation chain transfer (RAFT) polymerization technique, and then allowing the surface modifying agent to covalently bond with a functional group on the surface of the ophthalmic lens to immobilize the surface modifying agent onto the lens surface.